This invention is a further development to the commonly owned inventions of U.S. Pat. Nos. 5,788,335 and 5,810,451, the disclosures of which are incorporated herein by reference.
Whereas the concept has been developed wherein a tire is provided with an efficient way to extend and retract a tread portion, e.g., carrying studs, the present invention is directed to a process for the efficient incorporation of that concept to state of the art vehicle tires.
Tires have undergone impressive development over the years. Fifty years ago a tire wasn't expected to last for much more than 10,000 miles of driving. Even then blow outs were common occurrences and such were considered a major hazard of driving. Today a blow out is almost unheard of and a set of tires can last in excess of 80,000 miles.
Reference is made to FIG. 1 which illustrates the structure of a state of the art tire. The tire consists of two parts which are referred to as the casing 10 and the tread 12. The casing is a continuous wall from a first bead 14 to an opposite bead 16 at the respective sides of the casing. The beads fit the tire rim (not shown) which closes off the inner opening 18. The casing is a composite of steel fibers and tough rubber and will withstand very substantial abuse.
The casing material is hard and will not adequately grip a roadway as necessary to achieve traction. That is the job of the tread 12. The tread is a relatively soft rubber that provides the desired grip. The tread is adhered to the casing by a molding process. The uncured rubber is laid inside a mold that is shaped to form the desired tread design. The casing is abutted against the uncured rubber and the molding apparatus applies pressure and heat to cure the rubber 12 and bond it securely to the casing. With the tire removed from the mold, the tread design has been permanently molded into the exterior face 20.